Threaded connection for internally clad pipe

ABSTRACT

A corrosion-resistant threaded connection including a first tubular member having an outer metal tube of corrosion-prone material and an inner metal lining of corrosion-resistant material, the first tubular member forming a pin connection having a nose portion comprising a ring of corrosion-resistant material secured, e.g., welded, to the tube of corrosion-prone material, a radially outwardly facing, annularly extending thread-free first pin shoulder being formed on the corrosion-resistant ring, the first member including an externally threaded portion providing male threads, and a second tubular member comprising a metal coupling having a first end and a second end and forming a first box connection and a second box connection, respectively, the coupling including an internally disposed annularly extending metal section of corrosion-resistant material disposed intermediate the ends of the coupling, each of the box connections comprising a radially inwardly facing, annularly extending box shoulder formed on the section of corrosion-resistant material, each of the box connections further including a threaded female portion having threads complementary to the male threads, the pin and box shoulders being sized and configured such that when first and second of the first tubular members are threadedly received in the first and second box connections, respectively, the pin and box shoulders are in metal-to-metal sealing engagement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to threaded pipe connections and, moreparticularly, to a corrosion-resistant threaded connection assembliesfor use with clad pipe such as can be used as oil and gas well tubingand casing, piping in chemical and other plants, oil and gas pipelines,and the like.

2. Description of the Prior Art

There are numerous instances where piping and pipelines are used fortransporting fluids that are highly corrosive to materials such ascarbon steel from which such pipe and pipelines are typically made. Inparticular, in the production of oil and gas, there is a growing needfor corrosion-resistant alloy pipe, e.g., tubing, because of thecontinuing increase in the drilling of oil and gas wells into pay zonesthat produce highly corrosive fluids. To overcome the corrosionproblems, and as well known to those skilled in the art, it is common touse lined steel pipe, which liners may be made of plastic, stainlesssteel, or other corrosion-resistant materials.

A typical multiple-walled composite pipe, e.g., a lined steel pipe, is adual or double-walled pipe in which the inner wall is a liner tube madeof a corrosion-resistant material e.g., stainless steel, or some othercorrosion-resistant material (metal alloy) that serves as a conductorfor the corrosive fluid, and an outer wall or pipe that iscorrosion-prone, e.g., carbon steel and that is designed to providestrength to withstand the internal pressures of the corrosive fluid, aswell as external forces such as external pressure, mechanical loading,etc.

Obviously, particularly in the case of tubing or casing, there arelimitations on the length of such double-walled pipes due to conditionsto which the pipes are subjected on site. Thus, in the case of tubing orcasing strings and in the production of oil and gas, each joint of pipeis usually about 30-40 feet long while the tubing or casing stringitself may be thousands of feet long. Accordingly, and as is well knownin making up such tubing or casing strings, successive joints oftubing/casing are connected together using couplings until the desiredlength of string is achieved.

Typically, in these multiple-walled composite pipes, the inner tube orliner made of the corrosion-resistant material does a highly effectivejob of protecting the corrosion-prone outer tube or pipe. Indeed,methods of successively internally cladding corrosion prone pipe with acorrosion-resistant material are well known to those skilled in the art.The problem is not with the clad pipe, but rather where successivejoints of the clad pipe are adjoined to one another by means of acoupling. For many years, the goal has been to create a "holiday-free"interface at the junction of the clad pipe and the coupling. It servesno purpose to connect clad pipe utilizing a coupling that is subject tocorrosion since such a connection will sooner or later fail because thecoupling will fail.

The prior art is replete with pipe couplings and assemblies ostensiblydesigned to overcome the problem of eliminating corrosive attack at thejunction of the pipe and the coupling. However, insofar as is known toApplicants, none of these solutions have been readily embraced by theoil and gas industry, either because of cost factors, failures caused bycorrosion, or lack of sufficient structural integrity at thepipe/coupling juncture.

In U.S. Pat. No. 5,282,652, there is disclosed a corrosion-resistantpipe coupling structure comprising a tubular coupling member havingaxially opposite ends thereof. Internal screw threads form boxes thatengage male screw threads forming pins provided on the axially opposingend parts of two pipes to be connected, the internal surface of each ofthe pipes being resistant to corrosive fluids. An intermediate annularprojection is provided on the inner surface of the coupling member anddirected radially inwardly thereof to be abuttingly interposed betweenthe opposing end parts of the pipes. The structure is characterized inthat the intermediate annular projection is made of acorrosion-resistant material, at least in a radially intermost partthereof.

U.S. Pat. No. 4,026,583 also discloses corrosion-resistant tubing orcasing for use in the oil and gas industry.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acorrosion-resistant threaded connection assembly comprising a firsttubular member having an outer tube of corrosion-prone material, e.g.,carbon steel, and an inner lining of corrosion-resistant material, e.g.,stainless steel or some other corrosion-resistant metal alloy, the firsttubular member including a pin connection. The pin connection comprisesa nose portion formed of a ring of corrosion-resistant material, e.g., ametal alloy, secured to the tube of corrosion-prone material, therebyforming an annular securing locus. The ring of corrosion-resistantmaterial defines an annular, axially facing end surface and a radiallyoutwardly facing, annularly extending thread-free shoulder formed on thecorrosion-resistant ring and an axially extending, externally threadedportion providing male threads and extending axially inwardly of the pinshoulder and end surface, the securing locus being disposed intermediatethe end surface and the end of the externally threaded portion distalthe end surface. The assembly further includes a second tubular membercomprising a coupling having a first end and a second end, the couplinghaving a first box connection formed in the first end and a second boxconnection formed in the second end. The coupling further includes aninternally disposed annularly extending section of corrosion-resistantmaterial disposed intermediate the first and second ends of thecoupling. Each of the box connections comprises a radially inwardlyfacing, annularly extending box shoulder formed on the section ofcorrosion-resistant material. Each of the box connections furtherincludes an axially extending, internally threaded portion providingfemale threads complementary to the male threads and extending axiallyoutwardly of the thread-free box shoulder. The pin and box shoulders aresized and configured such that when first and second of the pinconnections are threadedly received in the first and second boxconnections, respectively, the pin and box shoulders are inmetal-to-metal sealing engagement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half-sectional, elevational view of one embodiment of theassembly of the present invention;

FIG. 2 is an enlarged fragmentary portion of FIG. 1 showing inparticular the engagement between the corrosion-resistant materials onthe pin ends and the coupling;

FIG. 3 is a view similar to FIG. 2 showing the incorporation of adeformable seal ring in the assembly;

FIGS. 4-6 are half-sectional, elevational views showing sequentially howone embodiment of the coupling of the present invention is formed;

FIGS. 7-9 are half-sectional, elevational views showing how the threadedpin members of the assembly of the present invention are formed;

FIG. 10 is a fragmentary, half-sectional, elevational view showing onepin connection made up to one of the boxes in the coupling and showingengagement of the nose of the pin connection with a torque or makeupshoulder formed in the coupling;

FIG. 11 is a view similar to FIG. 10 showing the connection of FIG. 10placed in tension such as would be encountered in a tubing or casingstring such as would be used in an oil or gas well;

FIG. 12 is a fragmentary, half-sectional, elevational view showinganother embodiment of the assembly of the present invention;

FIG. 13 is a fragmentary, half-sectional, elevational view showinganother embodiment of the assembly of the present invention;

FIG. 14 is a view similar to FIG. 1 showing another embodiment of theassembly of the present invention;

FIG. 15 is a view similar to FIG. 1 showing another embodiment of theassembly of the present invention; and

FIG. 16 is a fragmentary, half-sectional, elevational view showinganother embodiment of the assembly of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2, there is shown a corrosion-resistantthreaded connection assembly according to the present inventioncomprising a coupling, shown generally as 10, and described more fullyhereafter, and first and second tubular members or pipes, which could betubing or casing, shown generally as 12 with pin connections (pins)shown generally as 12a described more fully hereafter.

Coupling 10 comprises a tubular member 14 having a first box end 16 withtapered, female threads 18 and a second box end 20 having tapered femalethreads 22. Coupling 10 further includes an annular insert, showngenerally as 24, of corrosion-resistant material that is secureinternally of tubular member 14 by ways well known to those skilled inthe art and discussed hereinafter. Insert 24 defines a first, annularlyextending conical thread-free box shoulder 26 and a second, annularlyextending conical thread-free box shoulder 28. Insert 24 also forms anannular, radially inwardly projecting rib 30, rib 30 defining a first,annular axially facing abutment 32 and a second annular, axially facingabutment 34.

Pipes 12 are substantially the same in construction and comprise anouter tube 36 of a corrosion-prone material, e.g., carbon steel or thelike, and an inner metal lining or liner of corrosion-resistant material38, lining 38 being secured to tube 36 by methods well known to thoseskilled in the art and described more fully hereinafter. It will beunderstood that lining 38 extends for the full length of pipe 12. Asnoted, each of pipes 12 form a pin connection 12a having a nose portionformed of a ring 40 of corrosion-resistant material that is secured asby welding, as at 42, to tube 36, weld 42 forming an annular weld locusbetween ring 42 and pipe 36. Ring 40 further includes a radiallyoutwardly facing, annularly extending, conical, thread-free pin shoulder44 for a purpose hereinafter described. Ring 40 also defines an axiallyfacing, annularly extending end surface 46. As can be seen, particularlywith reference to FIG. 2, rib 30 is of a dovetail configuration and endsurfaces 46 on pins 12a are complementarily shaped. Each of pins 12afurther includes a tapered male threaded portion 48 extending axiallyoutwardly of pin shoulder 44. It can thus be seen that when pipes 12 arereceived in coupling 10 such that threads 48 on first pin 12a andthreads 18 in first box end 16 and threads 48 on second pin 12a andthreads 22 in second box end 20 are threaded together, and when endsurfaces 34 on pins 12a engage abutments 32 and 34 to the desired makeuptorque, forming "torque shoulders," the coupling 10 and the pins 12awill be in metal-to-metal sealing engagement. To this end, shoulders 26and 44 with respect to first box end 16 and 28 and 44 with respect tosecond box end 20 are sized and configured such that when the pins 12aare threadedly received in the coupling 10, shoulders 26 and 44 in thefirst box end form an interference, metal-to-metal seal, and likewiseshoulders 28 and 44 in the second box end form an interference,metal-to-metal seal. It will thus be appreciated that a "holiday-free"zone has been created at the juncture of the pipes 12 and the coupling10 in that in order for any corrosion-prone material to be exposed tocorrosive fluids passing through pipes 12 and coupling 10, such fluidmust leak past the metal-to-metal seals formed by the engaged shoulders26, 44, and 28, 44. In other words, the flowing corrosive fluid seesonly corrosion-resistant material, not only internally of the pipes 12with respect to the lining 38, but also with respect to any of thecomponents making up the threaded connection comprised of coupling 10and the pins 12a formed on pipes 12. As noted above, it is importantthat the juncture of the pipes 12 and the coupling 10 be constructed insuch a fashion that any corrosive fluids passing through pipes 12 andcoupling 10 be prevented from contacting any corrosion-prone materialmaking up either pipes 12 or coupling 10. Thus, for example, whatevertechnique is used to secure ring 40 to pipe 12 must eliminate thepossibility that there will be any corrosion-prone material disposedbetween lining 38 and ring 40 so that corrosive fluids can pass thejuncture of lining 38 and ring 40 and get between lining 38 and tube 36.Accordingly, any method or technique used to secure ring 40 to pipes 12will ensure that corrosion-resistant material spans any securing zone orlocus between lining 38 and ring 40. This can be accomplished, forexample, by using corrosion-resistant weld or brazing material In yetanother technique, lining 38, prior to the time that ring 40 is attachedto pipes 12, can be flared over the end of outer pipe 36 adjacent the IDand corrosion-resistant weld material used to form the securing locusbetween the ring 40 and lining 38 to ensure that there is no portion ofcorrosion-prone material forming pin 12a that is exposed to anycorrosive fluid.

While as described above, ring 40 is secured to pipe 12 by means ofwelding, it will be appreciated that other techniques for securing ring40 to pipe 12 can be used, i.e., the annular securing locus between ring40 and pipes 12 can be formed by welding, brazing, or, in certain cases,with special adhesives that are not affected by any corrosive fluids.For example, the securing locus might be formed by an annular wafer ofmaterial disposed between ring 40 and the end of pipe 12, which can, bymeans of proper treatment, fuse, or form with ring 40 and pipe 12 someother kind of fluid-tight bond, e.g., an intramolecular bond, betweenring 40 and pipe 12. As noted hereafter, ring 40, when the connection isfully made up--i.e., when coupling 10 and first and second pins 12a arethreadedly received therein--is under compressive loading, which greatlyexpands the types of securing techniques and securing agents that can beemployed to form the securing locus. While the securing locus, in thiscase described as weld 42, is simply shown as a line joint between ring40, on the one hand, and pipe 36 and lining 38, on the other hand, itwill be appreciated that this is for simplicity only and that thesecuring locus, e.g., the weld locus, can have a significant axialthickness depending upon the securing agent and/or securing techniqueemployed. Another securing technique that can be advantageously employedin securing the corrosion-resistant ring 40 to the pipe 12 can beaccomplished by a technique that employs temperatures below which thereis no effect on the metallurgical properties of the ring and the pipe.Whatever the nature of the securing locus and/or the method used toachieve it, there must result a liner (38), pin (36), ring (40) juncturethat is corrosion-resistant.

With respect to FIG. 3, there is shown a modification of the embodimentshown in FIGS. 1 and 2, wherein there are incorporated deformable sealrings 50 and 52, rings 50 and 52 being disposed in recesses 54 and 56formed in first and second box ends, respectively. Seal rings 50 and 52further ensure that any corrosive fluids that leak past themetal-to-metal seals will be prevented from contacting the interengagedthreaded portions of the connection, which, as can be seen for the mostpart, are formed of corrosion-prone material.

Attention is now directed to FIGS. 4-6, which show how a coupling foruse in the assembly of the present invention can be constructed.Disposed in a tubular blank 60 is a corrosion-resistant, annular section62 of corrosion-resistant material, annular section 62 generally beingsecured interiorly of tubular blank 60 by methods discussed hereinafter.Tubular blank 60 and corrosion-resistant section 62 are then machined,as shown in FIG. 5, to provide an unthreaded coupling preform 10a havingan unthreaded corrosion-resistant insert preform 24a. Followingthreading, in the well-known manner, and as shown in FIG. 6, oneachieves coupling 10 comprised of threaded tubular member 14 containinginsert 24, identical to that shown in FIG. 1. While FIGS. 4-6 showconstruction of a coupling that is a composite, i.e., formed of thetubular blank 60 of a corrosion-prone material and an annular section 62of corrosion-resistant material, it will be appreciated that theoperations depicted in FIGS. 4-6 could be carried out to produce acoupling that is made entirely of corrosion-resistant material ratherthan the composite shown in FIGS. 4-6. In other words, the tubular blank60 and an annular section 62 could comprise a monolith ofcorrosion-resistant material. Nonetheless, essentially the samemachining/threading operations shown in FIGS. 4-6 would be conducted onthe monolith.

FIGS. 7, 8, and 9 show a typical sequence of steps in forming the pinconnections 12a of pipe 12. A tubular blank 64 formed of an outer tubeof corrosion-prone material such as carbon steel 66 and an innercorrosion-resistant lining 38 is welded as by friction-welding or someother suitable welding technique, to an annular corrosion-resistant ring68, the weld being indicated at 70. Following the securing of ring 68 totubular blank 64, machining is conducted to provide a pin connectionpreform 64a, which results, as shown, in tube 66, being formed into atapered tube 66a. Additionally, corrosion-resistant ring 68 is machinedto provide a pin nose preform 68a, thread-free shoulder 44 being formedin such machining step. Lastly pin preform 64a is threaded to form pinconnection 12a.

FIGS. 10 and 12 demonstrate two conditions of the assembly of thepresent invention, FIG. 10 showing the assembly made up, i.e., the pinconnections threadedly received in the coupling, and in a "relaxed"condition, i.e., there being no axial forces acting on the assemblyother than as imposed by the interengaged threads. FIG. 11 shows theconnection of FIG. 10 in a typical condition such as would beexperienced in an oil and gas well when a "string" of tubing or casingemploying the threaded connection of the present invention is employedto connect successive joints of tubing, casing, or the like. As can beseen by the arrows A and B, the tension forces indicated by arrows A andB are transmitted from one pipe joint 12 to the successive pipe joint 12through the coupling 10 by virtue of the interengaged threads 48 on thepins 12a with the threads 18, 22 in the coupling 10. This tensionloading, if sufficiently high enough, will separate the abutment 32formed on the rib 30 from the end surface 46 formed on the first pinconnection 12a. Such separation is shown in exaggerated form in FIG. 11,it being understood that a like separation would occur between abutment34 and end surface 46 formed on the second pin connection 12a. However,even though such separation of the torque shoulders may occur, theconnection remains sealed because of the metal-to-metal, interferenceseal between shoulders 26 and 44. It will be understood that while onlythe first box end 16 is being described, a like situation applies withrespect to the second box end 20.

As can be seen from FIGS. 10 and 11, the weld zone 42 is disposedintermediate threads formed on the pin 12a such that at least the lastthread closest the nose of the pin 12a is formed primarily at least ofcorrosion-resistant material forming ring 40. Positioning the securingor weld zone or locus between engaged threads helps to maintain theloading in tension on the assembly across that zone or locus to aminimum. While the embodiment of FIG. 11 shows the weld locus 42 beingdisposed generally between the first thread on the pin nose 12a and thenext adjacent thread, FIG. 13 shows a condition where the weld locus hasbeen moved further away from the nose of pin 12a, i.e., further into thethreaded area. Thus, with reference to FIG. 13, ring 40a, shown ashaving a larger axial length than ring 40, is secured to pipe 36 by aweld zone 42a disposed generally in the area of the third and fourththreads on pin 12b, i.e., the weld zone is further up in the threadedzone. In general, it is preferred that the securing zone, e.g., weldzone, be disposed in the threaded area such that it lies betweenadjacent engaged threads since, as noted, this tends to maintain theloading in tension on the assembly across the securing zone to aminimum. Moving the securing zone further into the threaded area willgenerally mean that the axial length of the ring 40a is increased; e.g.,compare the axial length of ring 48 with the axial length of ring 40.This is clearly desirable since such added axial length has theadvantage that if the nose of the pin formed by the corrosion-resistantring 40 or 40a is damaged, there is sufficient material remaining suchthat, with proper machining and threading, a new pin nose 12a can beformed without the necessity of having to add an entirely newcorrosion-resistant ring.

With reference to FIG. 12, there is shown another embodiment of theassembly of the present invention wherein corrosion-resistant ring 40bis secured to pin 12c at a weld zone 42b, which is on the pin nose sideof the first thread of pin connection 12c, i.e., the weld zoneessentially lies in the thread-free zone and, more particularly,approximately at the start of the thread-free pin flank 44a. It will beapparent that in the embodiment shown in FIG. 12 with the weld zone outof the threaded portion of the connection, once the connector is madeup, the weld zone 42b is placed in compression. In essence, ring 40b isessentially in a neutral state because the coupling 10, which transmitsthe tension between successive joints of pipe 12, has no effect on ring40b in the sense that it is not exerting a significant pulling force onring 40b. It will be appreciated that one of the features of the presentinvention is the fact that for all intents and purposes, thecorrosion-resistant ring, e.g., ring 40, forming the nose of the pin isessentially placed in compression when the assembly comprising thecoupling 10 and the pipes 12 are made up to full makeup torque. Thisclearly minimizes the chances that the corrosion-resistant ring will beseparated from the pipe 12 since, for all intents and purposes, theforces acting on the corrosion-resistant ring are tending to force thosetwo members together. This unique construction places thecorrosion-resistant rings under compressive loading, and as noted above,provides an expanded variety of securing techniques and agents, e.g.,welding, brazing, etc., that can be used to secure thecorrosion-resistant rings to the pipes.

Reference is now made to FIG. 14, which shows another embodiment of theconnection assembly of the present invention. The assembly shown in FIG.14, indicated generally as 90, is what is referred to in the industry asa stepped thread design. The coupling, shown generally as 92, comprisesa tubular member 94 having a corrosion-resistant, annular insert 96disposed generally centrally therein. There are thus defined first andsecond box connections 98 and 100, respectively. First box connection 98is provided with a first, tapered, axially extending, internallythreaded female portion 102 and a second axially extending, internallythreaded female portion 104, threaded portions 102 and 104 being axiallyspaced from one another and separated by a makeup or torque shoulder 74.As in the case of box connection 98, box connection 100 is likewiseprovided with a first, axially extending, internally threaded femaleportion 108 and a second, axially extending internally threaded femaleportion 110, threaded sections 108 and 110 being displaced axially fromone another and separated by a torque or makeup shoulder 112. So-calledstepped threads as described above having makeup or torque shouldersseparating the axially spaced stepped threaded portions are well knownand are shown, for example, in U.S. Pat. Nos. 4,161,332 and 4,192,533and patents referenced therein, all of which are incorporated herein byreference for all purposes. Insert 99 is provided with a first annular,radially inwardly extending surface 114 in box 98 and a second annular,radially inwardly extending sealing surface 116 in box 100.

The assembly shown in FIG. 14, as those described above, furtherincludes an elongate tubular member 118 comprising an outer pipe 120 ofcorrosion-prone material and an inner lining 122 of corrosion-resistantmaterial. As in the manner described above with respect to ring 40 andpipe 36, pipe 120 is secured to an annular ring 124 ofcorrosion-resistant material, ring 124 being provided with an annularlyextending, radially outwardly facing sealing surface 126. Tubular member118 forms a pin connection 128 formed by a first threaded male portion130 and a second threaded male portion 132, threaded male portions 130and 132 being axially spaced from one another, a first annular, axiallyfacing makeup shoulder 134 being formed between threaded male portions130 and 132. It will thus be apparent that when first and second pinconnections 128 are received in boxes 98 and 100, respectively, andmakeup shoulders 106 and 134, on the one hand, and makeup shoulders 134and 112, on the other hand, are engaged to the desired torque, ametal-to-metal seal will be formed between annular sealing surfaces 114and 126 in box connection 98 and between sealing surfaces 116 and 126 inbox connection 100. Once again, it will be seen that any corrosivefluids being carried through the connection assembly will "see" nothingbut corrosion-resistant material inasmuch as the corrosion-proneportions of the assembly are protected from attack by the corrosivefluid by virtue of the corrosion-resistant lining 122, thecorrosion-resistant insert 96, and the corrosion-resistant rings 124.

With reference to FIG. 15, there is shown a slightly modified embodimentof the assembly shown in 14, the embodiment shown in 15 differing fromthat shown in FIG. 14 only in the fact that the entire coupling 92a isformed of corrosion-resistant material rather than being formed, ascoupling 92, of a corrosion-prone tubular member 94 and an insert ofcorrosion-resistant material 96.

With reference now to FIG. 16, there is shown yet another embodiment ofthe connection assembly of the present invention. In the embodimentshown in FIG. 16, coupling 10c is similar to coupling 10 with theexception that insert 24b, rather than having an annular rib such as rib30, shown in FIGS. 1-3, is provided with a rib 30b, which is notundercut and which rather is provided with abutment surfaces 32a and34a, which are axially facing and which lie generally in planesperpendicular to the axis passing axially through the connectionassembly. As can also be seen, abutment surfaces 32a and 34a do not formtorque or makeup shoulders. In this regard, annular ring 40b is formedwith an end surface 46a, which is annular and axially facing and whichgenerally lies in a plane perpendicular to the long axis of theconnection assembly. It will be seen that rather than being in contact,surfaces 24b and 46a with respect to the first box connection andsurfaces 34a and 46a with respect to the second box connection are notin engagement, leaving a gap. However, since annular seal surfaces 26and 44 are in metal-to-metal interference or sealing engagement, allcorrosion-prone portions of the connection assembly are protected fromattack by corrosive fluids flowing through the connection assembly.

Except for the embodiment shown in FIG. 16, most of the embodiments ofthe present invention have been described with reference to an internalshoulder formed between the noses of the pins 12a and a rib similar torib 30 formed in the coupling 10. FIG. 16 demonstrates that suchshouldering, while clearly desirable, is not a necessary limitation ofthe threaded connection of the present invention. Indeed, the threadedconnection of the present invention can be constructed without annularribs similar to rib 40, i.e., in such a manner that there is no portionof the coupling 10 that protrudes radially inwardly between theinnermost ends of the pins 12a. Nonetheless, any such connection wouldhave the metal-to-metal radial seals such as are formed by engagedshoulders 26, 44 and 28, 44, for example. It will also be appreciated bythose skilled in the art that torque or makeup shoulders that areexternal to the connection assembly can be employed. Indeed, as shown inFIG. 14, in the case of a stepped thread design, such makeup or torqueshoulders can be formed intermediate axially spaced stepped threadedportions. Whatever form or position of torque or makeup shoulder isemployed, a feature of the present invention is the provision formetal-to-metal sealing between a radially outwardly facing, annularlyextending surface or shoulder on the pin or male member and a radiallyinwardly facing, annularly extending surface or shoulder in the boxconnection formed in the coupling. Although the metal-to-metal seals areshown as being formed by the engagement of frustoconical surfaces, itwill be appreciated that the invention is not so limited and that othercomplementarily shaped surfaces that can be forced into metal-to-metalsealing engagement can be employed.

It will be apparent that many modifications of the above invention notexpressly described can be made. For example, and as shown, torqueshoulders are not necessarily needed. Additionally, deformable sealrings can be used in the embodiments shown in FIGS. 14 and 15 andvarious thread forms can be used in any of the embodiments. It will beappreciated that the corrosion-resistant materials of the presentinvention can take many forms. Thus, for example, various linercompositions may be employed, depending upon the corrosiveness of thefluid being handled. For example, high alloy materials such as HastelloyC, Iconel 625 may be used for extremely aggressive and corrosiveenvironments, whereas lesser alloy-containing steels such as 26 Cr-1-Mo,28 Cr-4-Mo, 17-4-PH, and Carpenter 450 can be used for less aggressiveenvironments such as those containing chlorides, wet carbon dioxide, orthe like. It will also be appreciated that the radial thickness of thecorrosion-resistant liner can vary depending upon the material employedand the degree of corrosiveness of the fluids being handled.

Bonding between the corrosion-prone pipe and the corrosion-resistantliner and/or between the coupling and corrosion-resistant insert can beachieved by numerous methods well known to those skilled in the art andas exemplified in U.S. Pat. No. 4,026,583, incorporated herein byreference for all purposes. Accordingly, the bond between the pipe andthe liner may be a braze bond, as, for example, which may be achieved byheating of the liner to brazing temperatures, in which case the linerouter surface would have a liquefying temperature substantially lowerthan that of the corrosion-prone pipe. As an example, the liner couldinclude a metallic outer coating such as copper, which liquefies at arelatively low temperature and, which once liquified, would bond thecorrosion-resistant liner to the corrosion-prone pipe. In still anothermanner, the bond between the liner and the corrosion-resistant pipe canbe achieved by internally pressuring the liner to cause it to weld tothe corrosion-prone pipe, the material of the liner diffusing into themetal of the corrosion-prone pipe. Such pressure may be created by anexplosion within the liner or by a pressurizing liquid contained withinthe liner, as more fully disclosed in U.S. Pat. No. 4,026,583. The linerand/or insert may also be shrink-fitted into the pipe and/or coupling,respectively.

The foregoing description and examples illustrate selected embodimentsof the present invention. In light thereof, variations and modificationswill be suggested to one skilled in the art, all of which are in thespirit and purview of this invention.

What is claimed is:
 1. A corrosion-resistant threaded connectionassembly comprising:a first tubular member comprising an outer metaltube of corrosion-prone material and an inner metal lining ofcorrosion-resistant material, said first tubular member comprising a pinconnection, said pin connection comprising a nose portion comprising aring of corrosion-resistant material secured to said tube ofcorrosion-prone material, forming an annular securing locus, said ringdefining an annular, axially facing end surface, said pin connectionfurther including a radially outwardly facing, annularly extendingthread-free pin shoulder formed on said corrosion-resistant ring and anaxially extending, externally threaded portion providing male threadsand extending axially inwardly of said pin shoulder, said securing locusbeing disposed intermediate said end surface and the end of saidexternally threaded portion distal said end surface; a second tubularmember comprising a metal coupling having a first end and a second end,said coupling having a first box connection formed in said first end anda second box connection formed in said second end, said couplingincluding an internally disposed, annularly extending section ofcorrosion-resistant material disposed intermediate said first and secondends of said coupling, each of said box connections comprising aradially inwardly facing, annularly extending box shoulder formed onsaid section of corrosion-resistant material, each of said boxconnections further including an axially extending, internally threadedportion providing female threads complementary to said male threads andextending axially outwardly of said thread-free box shoulder; and saidpin and box shoulders being sized and configured such that when firstand second of said pin connections are threadedly received in said firstand second box connections, respectively, said pin and box shoulders arein metal-to-metal sealing engagement, at least a portion of the firstone of said male threads being formed on said ring ofcorrosion-resistant material.
 2. The assembly of claim 1 wherein saidring of corrosion-resistant material is thread-free.
 3. The assembly ofclaim 1 wherein said section of corrosion-resistant material defines anannular, radially inwardly extending rib between said first and secondbox connections.
 4. The assembly of claim 3 wherein said rib assemblyforms a first annular, axially facing abutment in said first boxconnection and a second annular, axially facing abutment in said secondbox connection.
 5. The assembly of claim 4 wherein when said first andsecond pin connections are received in said first and second boxconnections, respectively, said axially facing end surface on said firstpin connection is in engagement with said first abutment in said firstbox connection and said axially facing end surface on said second pinconnection is in engagement with said second abutment in said second boxconnection.
 6. The assembly of claim 5 wherein each of said abutmentsforms an undercut surface and said end surface of each of said pinconnections is complementarily shaped.
 7. The assembly of claim 1wherein said coupling is made entirely of corrosion-resistant material.8. The assembly of claim 1 wherein said coupling comprises an outertubular portion of a corrosion-prone material and an inner, annularinsert of corrosion-resistant material, said corrosion-resistant sectionbeing formed by said insert.
 9. The assembly of claim 8 wherein saidinsert is welded to said outer tubular portion of said coupling.
 10. Theassembly of claim 1 wherein said externally threaded portion on saidfirst tubular member defines a first two-step thread and each of saidinternally threaded portions in said second tubular member defines asecond two-step thread, complementary to said first two-step thread. 11.The assembly of claim 10 wherein said first two-step thread defines afirst threaded male portion and a second threaded male portion, axiallyspaced from said first threaded male portion, an annular, axiallyfacing, pin makeup shoulder being formed between said first and secondthreaded male portions and each of said second two-step threads definesa first threaded female portion and a second threaded female portion,axially spaced from said first threaded female portion, a first annular,axially facing makeup shoulder being formed between said first andsecond threaded female portions in said first box connection, a secondannular, axially facing makeup shoulder being formed between said firstand second threaded female portions in said second box connection, saidpin makeup shoulders and said first and second makeup shoulders beingengaged when first and second pin connections are threadedly received insaid first and second box connections, respectively.
 12. The assembly ofclaim 11 wherein said pin makeup shoulder is undercut and said first andsecond makeup shoulders are complementarily shaped.
 13. The assembly ofclaim 1 wherein one of said first tubular member or said second tubularmember includes an annularly extending receiving formation for adeformable seal ring, and there is a deformable seal ring disposed insaid receiving formation, said receiving formation and said seal ringbeing positioned such that such seal ring effects sealing between theinterior of said second tubular member and the exterior of said firsttubular member.
 14. The assembly of claim 1 wherein said securing locusis disposed in said externally threaded portion.
 15. Acorrosion-resistant threaded connection assembly comprising:a firsttubular member comprising an outer metal tube of corrosion-pronematerial and an inner metal lining of corrosion-resistant material, saidfirst tubular member comprising a pin connection, said pin connectioncomprising a nose portion comprising a ring of corrosion-resistantmaterial secured to said tube of corrosion-prone material, forming anannular securing locus, said ring defining an annular, axially facingend surface, said pin connection further including a radially outwardlyfacing, annularly extending thread-free pin shoulder formed on saidcorrosion-resistant ring and an axially extending, externally threadedportion providing male threads and extending axially inwardly of saidpin shoulder, said securing locus being disposed intermediate said endsurface and the end of said externally threaded portion distal said endsurface; a second tubular member comprising a metal coupling having afirst end and a second end, said coupling having a first box connectionformed in said first end and a second box connection formed in saidsecond end, said coupling including an internally disposed, annularlyextending section of corrosion-resistant material disposed intermediatesaid first and second ends of said coupling, said section ofcorrosion-resistant material defining the entirety of an annular,radially inwardly extending rib between said first and second boxconnections, each of said box connections comprising a radially inwardlyfacing, annularly extending box shoulder formed on said section ofcorrosion-resistant material, each of said box connections furtherincluding an axially extending, internally threaded portion providingfemale threads complementary to said male threads and extending axiallyoutwardly of said thread-free box shoulder; and said pin and boxshoulders being sized and configured such that when first and second ofsaid pin connections are threadedly received in said first and secondbox connections, respectively, said pin and box shoulders are inmetal-to-metal sealing engagement.
 16. The assembly of claim 15 whereinat least a portion of the first one of said male threads is formed onsaid ring of corrosion-resistant material.
 17. The assembly of claim 15wherein said ring of corrosion-resistant material is thread-free. 18.The assembly of claim 15 wherein said rib assembly forms a firstannular, axially facing abutment in said first box connection and asecond annular, axially facing abutment in said second box connection.19. The assembly of claim 18 wherein when said first and second pinconnections are received in said first and second box connections,respectively, said axially facing end surface on said first pinconnection is in engagement with said first abutment in said first boxconnection and said axially facing end surface on said second pinconnection is in engagement with said second abutment in said second boxconnection.
 20. The assembly of claim 19 wherein each of said abutmentsforms an undercut surface and said end surface of each of said pinconnections is complementarily shaped.
 21. The assembly of claim 15wherein said coupling is made entirely of corrosion-resistant material.22. The assembly of claim 15 wherein said coupling comprises an outertubular portion of a corrosion-prone material and an inner, annularinsert of corrosion-resistant material, said corrosion-resistant sectionbeing formed by said insert.
 23. The assembly of claim 22 wherein saidinsert is welded to said outer tubular portion of said coupling.
 24. Theassembly of claim 15 wherein said externally threaded portion on saidfirst tubular member defines a first two-step thread and each of saidinternally threaded portions in said second tubular member defines asecond two-step thread, complementary to said first two-step thread. 25.The assembly of claim 24 wherein said first two-step thread defines afirst threaded male portion and a second threaded male portion, axiallyspaced from said first threaded male portion, an annular, axiallyfacing, pin makeup shoulder being formed between said first and secondthreaded male portions and each of said second two-step threads definesa first threaded female portion and a second threaded female portion,axially spaced from said first threaded female portion, a first annular,axially facing makeup shoulder being formed between said first andsecond threaded female portions in said first box connection, a secondannular, axially facing makeup shoulder being formed between said firstand second threaded female portions in said second box connection, saidpin makeup shoulders and said first and second makeup shoulders beingengaged when first and second pin connections are threadedly received insaid first and second box connections, respectively.
 26. The assembly ofclaim 25 wherein said pin makeup shoulder is undercut and said first andsecond makeup shoulders are complementarily shaped.
 27. The assembly ofclaim 15 wherein one of said first tubular member or said second tubularmember includes an annularly extending receiving formation for adeformable seal ring, and there is a deformable seal ring disposed insaid receiving formation, said receiving formation and said seal ringbeing positioned such that such seal ring effects sealing between theinterior of said second tubular member and the exterior of said firsttubular member.
 28. The assembly of claim 15 wherein said securing locusis disposed in said externally threaded portion.